Magnetic disk drives may be used for many different video applications. Examples include streaming media servers, digital hub devices such as TiVo, and TV studio and film production equipment.
When used for video, disk drives assign data blocks in one of two generally accepted paradigms: either in a round-robin sequence, or randomly.
The round robin placement uses a cycle based approach. This guarantees certain aspects of service quality. The random placement uses a deadline driven approach. This may have certain advantages such as delivery rate advantages with a single storage data block size, improved support for interactive applications and support for certain kinds of data reorganization. These latter applications may be supported with cycle based scheduling. However, cycle based scheduling may need to assume that certain disk parameters have their worst-case values. This can cause complexity and lack of efficiency.
Deadline driven scheduling can be configured efficiently in a way that encodes a low probability of disruptions. One important task includes limiting the number of streams to minimize the number of missed deadlines. This task is performed by the admission control part of the scheduler.